1. Field of the Invention
The invention relates to tandem systems for circuit-based traffic, and in particular, to tandem systems that use Asynchronous Transfer Mode (ATM) systems to interconnect various circuit-based networks or network elements.
2. Description of the Prior Art
The tandem function is used to concentrate and switch telecommunications traffic in between networks, switches, and other network elements. FIG. 1 depicts the conventional tandem switch known in the prior art. The three switches and the network element are all connected to the tandem switch. The tandem switch allows the switches to connect to the network element without a direct connection between the switches and the network element. It also allows each switch to connect to every other switch without direct connections between all of the switches. This savings in connections and trunking is one of the benefits of tandem switches. Additionally, the connection between the tandem switch and the network element uses bandwidth more efficiently because traffic has been concentrated at the tandem switch. In addition, a tandem switch can be used to concentrate traffic that is going to other networks.
The connections shown on FIG. 1 as solid lines are circuit-based connections. Circuit-based connections are well known in the art with some examples being Time Division Multiplex (TDM) connections, such as DS3, DS1, DS0, E3, E1, or E0 connections. DS3 connections carry a continuous transport signal at 44.736 megabits per second. DS1 connections carry a continuous transport signal at 1.544 megabits per second. DS0 connections carry a continuous transport signal at 64 kilobits per second. As is known, DS3 connections can be comprised of multiple DS1 connections, which in turn, can be comprised of multiple DS0 connections. The signaling links shown as dashed lines may be conventional signaling links with examples being SS7, C7, or ISDN links. The switches shown on FIG. 1 are well known circuit switches with examples being the Nortel DMS-250 or the Lucent 5ESS. The tandem switch is typically comprised of a circuit switch that interconnects DS3, DS1, and DS0 connections.
Those skilled in the art are aware of the costs and efficiencies associated with tandem switches. Many networks cannot justify implementing a tandem switch until the efficiencies gained through the tandem function outweigh the cost of the tandem switch. This is problematic because inefficiencies must be tolerated until they outweigh the high cost of the tandem switch. At present, there is a need for a more affordable and efficient tandem switching system.
The invention includes a telecommunications tandem system and method for providing a tandem connection for a call. The tandem system comprises a first ATM interworking multiplexer, an ATM cross-connect, a second ATM interworking multiplexer, and a signaling processor. The first ATM interworking multiplexer receives circuit-based traffic for the call from a first circuit-based connection. It converts the circuit-based traffic into ATM cells that identify a selected virtual connection based on a first control message and transmits the ATM cells. The ATM cross-connect is connected to the first ATM interworking multiplexer. It receives the ATM cells from the first ATM interworking multiplexer and routes the ATM cells based on the selected virtual connection identified in the ATM cells. The second ATM interworking multiplexer that is connected to the ATM cross-connect. It receives the ATM cells from the ATM cross-connect. It converts the ATM cells into the circuit-based traffic and transmits the circuit-based traffic over a selected second circuit-based connection based on a second control message. The signaling processor is linked to the first ATM multiplexer and the second ATM multiplexer. It receives and processes telecommunications signaling for the call to select the virtual connection and the second circuit-based connection. It provides the first control message for the call to the first ATM multiplexer and provides the second control message for the call to the second ATM multiplexer. The first control message identifies the first circuit-based connection and the selected virtual connection. The second control message identifies the selected virtual connection and the selected second circuit-based connection. As a result, the tandem connection is formed by the first circuit based connection, the selected virtual connection, and the selected second circuit based connection.
In various other embodiments. The tandem system provides the tandem connection for the call between: two circuit-based switches, two circuit-based switching networks, a circuit-based switch and an enhanced services platform, an incumbent local exchange carrier and a competitive local exchange carrier, a first competitive local exchange carrier and a second competitive local exchange carrier, a local exchange carrier and an interexchange carrier, for the call, a local exchange carrier and an international carrier, an interexchange carrier and an international carrier.
In various embodiments, the signaling processor selects the connections for the call based on: a call set-up message, a Signaling System #7 Initial Address Message (SS7 IAM), a called number, an NPA, an NXX, an NPA-NXX, a destination network, a transit network selection code, a carrier identification parameter, a nature of address, a network element identifier, a local route number, or a trunk group.
In various embodiments, numerous physical limitations may also distinguish the invention. The first ATM multiplexer and the second ATM multiplexer may be incorporated into a single ATM multiplexer. The first control message and the second control message may be incorporated into a single control message. The first ATM multiplexer, the second ATM multiplexer, and the ATM cross-connect may be physically located at the same site. The signaling processor, the first ATM multiplexer, the second ATM multiplexer, and the ATM cross-connect may be physically located at the same site.
Advantageously, the invention provides a tandem function between circuit based systems without the need for a circuit-based switch or an ATM switch. The invention is capable of accomplishing various forms of tandem routing without requiring a full set of complex routing logic. For example, the invention may only analyze a destination network code to select a tandem connection and could omit the need to analyze a called number. The invention is also capable of providing an ATM interface.